fs/ubifs: use rbtree postorder iteration helper instead of opencoding

Use rbtree_postorder_for_each_entry_safe() to destroy the rbtree instead
of opencoding an alternate postorder iteration that modifies the tree

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c
index 065096e..c14adb2 100644
--- a/fs/ubifs/recovery.c
+++ b/fs/ubifs/recovery.c
@@ -1335,29 +1335,14 @@
  */
 void ubifs_destroy_size_tree(struct ubifs_info *c)
 {
-	struct rb_node *this = c->size_tree.rb_node;
-	struct size_entry *e;
+	struct size_entry *e, *n;
 
-	while (this) {
-		if (this->rb_left) {
-			this = this->rb_left;
-			continue;
-		} else if (this->rb_right) {
-			this = this->rb_right;
-			continue;
-		}
-		e = rb_entry(this, struct size_entry, rb);
+	rbtree_postorder_for_each_entry_safe(e, n, &c->size_tree, rb) {
 		if (e->inode)
 			iput(e->inode);
-		this = rb_parent(this);
-		if (this) {
-			if (this->rb_left == &e->rb)
-				this->rb_left = NULL;
-			else
-				this->rb_right = NULL;
-		}
 		kfree(e);
 	}
+
 	c->size_tree = RB_ROOT;
 }